Compression molding is a manufacturing process used to fabricate a large variety of articles. In compression molding, raw material is typically placed into an open cavity in a first portion of a mold. The raw material, which may be rubber or some other type of thermosetting material, is typically in solid form. The raw material may be a single piece, may be in multiple pieces, or may even be a powder. A second portion of the mold is then attached to (or otherwise placed into contact with) the first portion. As heat and pressure are applied, the raw material in the mold cavity is formed into the desired shape.
Compression molding is often used when manufacturing footwear. In particular, midsoles, outsoles, and various other footwear components are frequently formed from rubber, plastic and/or other materials which are heated and pressed into desired shapes. FIGS. 1A-1C are partially schematic drawings of a typical procedure for compression molding footwear components according to the prior art. FIG. 1A shows a first mold 2 and a second mold 3 for a pair of shoe outsoles. Cavities 4 and 5 are formed in first mold 2. The bottom of cavity 4 corresponds to a bottom surface of a left shoe outsole, and the bottom of cavity 5 corresponds to a bottom of a right shoe outsole. Second mold 3 includes a pair of protrusions 6 and 7 which respectively correspond to the top surfaces of the left and right shoe outsoles.
One or more pieces of the raw material(s) for the outsoles are placed into each of cavities 4 and 5. As shown in FIG. 1B, second mold 3 is then placed on first mold 2 so that protrusions 6 and 7 extend into cavities 4 and 5, with spaces between the protrusions and the cavity walls forming mold volumes corresponding to the outsoles being produced. As seen in FIG. 1C, the joined molds are then placed between two platens 8 and 9 of a press. Platens 8 and 9 are then heated by source(s) internal to the platens. Heat from platens 8 and 9 is transferred to molds 2 and 3 as platens 8 and 9 are pressed together. The pressure and heat is maintained for a time sufficient for the raw material to fill the mold volumes and to set. Depending upon the material(s) being used, this may be several minutes or more.
Conventional compression molding equipment and methods (such as those described above) can present challenges. So as to withstand the pressing forces, platens are often substantial structures which contain large masses of metal. In order to transfer sufficient heat to the molds, a significant amount of heat must be applied to the platens. The platens may also be wider and/or longer than the molds (as seen in FIG. 1C). In such a case, the platens may be heated in areas which are not in contact with (and thus do not transfer significant heat to) the molds. These configurations can thus be thermally inefficient. Moreover, a relatively long amount of time may be needed to transfer sufficient heat from the platens to the molds. In addition to being inconvenient, extended heating times can slow production.
Conventional arrangements may also limit the precision with which mold heating can be controlled. Different types of materials must be heated to different temperatures. Because the heat source is relatively far from the molds in the arrangement of FIG. 1C, heating the molds within a specific temperature range may be difficult. Moreover, different molds may have different internal geometries. For example, some molds may be thicker in certain regions, and therefore require more heat in those regions to reach a desired temperature. Heating sources within the platens are usually in a fixed (and sometimes unknown) configuration. It may therefore be impractical to rearrange those heating sources based on the geometry of a particular mold.
Conventional platen-mold systems can also require excessive time to cool. Some materials (e.g., Phylon) require that the mold cool before the platens are released from the mold. Excessive cooling times can thus slow production when using such materials.
Yet another challenge presented by conventional compression molding techniques relates to handling of a mold before (and/or after) the mold is pressed. For many types of footwear, significant time is needed to prepare a mold for production. For example, certain shoe outsoles are formed from multiple types of material. This may be for aesthetic reasons (e.g., color “pops” for forming multicolored outsoles), for structural reasons (e.g., to place a harder or softer material in certain outsole regions), or for other reasons. When preparing to mold such an outsole, separate pieces of different raw materials must be carefully placed at the proper locations in the mold. Trimming of raw materials may also be needed. Arrangements which enhance an operator's ability to prepare one mold while another is being heated and pressed can increase productivity.